That's because you're looking at the wrong place, that's not the responsibility of REST: it can't because it's not a specification, but a description of an architectural style.
Instead, it's the responsibility of the media type. HTML offers hypermedia controls: hyperlinks are denoted with <a>, <area>, <base>, <link> elements and the "href" attribute; forms are denoted with the <form> element as its "action" attribute. I assume you are familiar with HTML, you can see that this is a very generalised way to find links (or controls in general), it is applicable to all HTML documents. XML has close analogues: XLink and XForms. JSON-done-right offers hypermedia controls: moral equivalent of links <https://datatracker.ietf.org/doc/html/draft-kelly-json-hal#s...>, moral equivalent of forms <https://rwcbook.github.io/hal-forms/>. It is easy to reimagine `application/vnd.github+json` in the guise of this media type so that the problem I was describing earlier disappears. If a media type cannot express hypermedia controls or link relations inline (e.g. WebP images), then the HTTP header can be used instead, see RFCs 8288 and 6570.
